Learning Objectives
Differentiate between pigmented skin disorders based on the presence, number, and function of melanocytes. Master the clinical triggers for Melasma and Vitiligo, and understand the embryological basis of Waardenburg syndrome.
1. Functional vs. Structural Pigment Loss
Pigment disorders can result from either a lack of melanin production or the physical destruction/absence of the cells that create it.
| Condition | Melanocyte Status | Pathophysiology | High-Yield Clinical Note |
|---|---|---|---|
| Albinism | Normal Number | Reduced melanin due to low tyrosinase activity or defective transport. | Significantly increased risk of skin cancer (SCC, BCC, Melanoma). |
| Vitiligo | Decreased/Absent | Autoimmune destruction of melanocytes. | Irregular patches of complete depigmentation are associated with other autoimmune diseases. |
2. Acquired Hyperpigmentation
Hyperpigmentation is often triggered by hormonal shifts, particularly in individuals with darker baseline skin tones.
| Condition | Triggers | Presentation |
|---|---|---|
| Melasma (Chloasma) | Pregnancy, OCP use, UV light. | Symmetrical “mask of pregnancy”; hyperpigmented macules on the face. |
3. Developmental Pigment Defects
Genetic defects in the migration of pigment-producing cells can lead to systemic findings beyond the skin.
| Condition | Embryologic Defect | Clinical Features |
|---|---|---|
| Waardenburg Syndrome | Defective neural crest cell differentiation. | Patchy depigmentation (skin/hair), heterochromia (different colored irises), and deafness. |
Activity:
High-Yield Mnemonics:
- Albinism: Albinism = All melanocytes are present, but Absent tyrosinase activity.
- Vitiligo: Vitiligo = Vanishing melanocytes (autoimmune).
- Neural Crest: If a question mentions melanocytes and deafness, think Neural Crest cells (Waardenburg).